Composites containing surface treated carbon microfibers

Abstract

A method of oxidizing the surface of carbon microfibers that includes contacting the microfibers with an oxidizing agent that includes sulfuric acid and potassium chlorate under reaction conditions sufficient to oxidize the surface. The invention also features a method of decreasing the length of carbon microfibers that includes contacting the microfibers with an oxidizing agent under reaction conditions sufficient to decrease the length.

We claim: 
     
       1. A composite comprising carbon microfibers in a matrix wherein the carbon microfibers have on an outer surface of the carbon microfiber a plurality of oxygen-containing groups or derivatives thereof. 
     
     
       2. The composite of claim 1 wherein said matrix comprises an organic polymer. 
     
     
       3. The composite of claim 1 wherein said matrix comprises an inorganic polymer. 
     
     
       4. The composite of claim 1 wherein said matrix comprises a metal. 
     
     
       5. The composite of claim 1 wherein said matrix comprises a ceramic material. 
     
     
       6. The composite of claim 1 wherein said matrix comprises an elastomer. 
     
     
       7. A composite according to claim 1. wherein the carbon microfibers comprises a multiplicity of fibrils having a fibril axis and a morphology consisting of tubes that are free of a continuous thermal carbon overcoat and have graphitic layers having a projection along the fibril axis, wherein the projection of the graphitic layers along the fibril axis extends at least two fibril diameters. 
     
     
       8. A composite according to claim 7, wherein the diameter of the fibrils is no greater than about 0.1 microns. 
     
     
       9. A composite according to claim 7, wherein the diameter of the fibrils is between about 3.5 and about 75 nanometers. 
     
     
       10. A composite according to claim 7, wherein the projection of the graphitic layers along the fibril axis extends at least 5 fibril diameters. 
     
     
       11. A composite according to claim 7, wherein the graphitic layers are parallel to the fibril axis. 
     
     
       12. A composite according to claim 11, wherein the oxygen-containing groups are selected from the group consisting of carbonyl, carboxylic acid, carboxylic acid ester, epoxy, vinyl ester, hydroxy, alkoxy, isocyanate, amide or derivatives thereof. 
     
     
       13. A composite comprising carbon fibrils in a matrix wherein the fibrils have a morphology consisting of tubes that are free of a continuous thermal carbon overcoat and have on an outer surface of the tubes a plurality of oxygen-containing groups or derivatives thereof, wherein the fibrils have a diameter no greater than about 0.1 microns. 
     
     
       14. A composite according to claim 13, wherein the diameter of the fibrils is between about 3.5 and about 75 nanometers. 
     
     
       15. A composite according to claim 13, wherein the oxygen-containing groups are selected from the group consisting of carbonyl, carboxylic acid, carboxylic acid ester, epoxy, vinyl ester, hydroxy, alkoxy, isocyanate, amide or derivatives thereof. 
     
     
       16. A composite according to claim 13, wherein said matrix comprises an organic polymer. 
     
     
       17. A composite according to claim 13, wherein said matrix comprises an inorganic polymer. 
     
     
       18. A composite according to claim 13, wherein said matrix comprises a metal. 
     
     
       19. A composite according to claim 13, wherein the carbon fibrils are prepared by introducing functional groups onto the surface of the carbon fibrils by contacting said carbon fibrils with an oxidizing agent that includes sulfuric acid and potassium chlorate to oxidize the surface of the carbon fibrils, for a period of time, at room temperature, insufficient to decrease the length of the carbon fibrils by chopping. 
     
     
       20. A composite according to claim 13, wherein the carbon fibrils are prepared by a method of decreasing a length of the carbon fibrils comprising contacting said carbon fibrils with an oxidizing agent, at room temperature, for a period of time sufficient to decrease the length of the fibrils by chopping.